This invention relates to an enthalpy calculator unit in which enthalpy is calculated by an arithmetic unit in accordance with an enthalpy equation from the temperature and relative humidity of humid air. The calculated enthalpy is converted into electrical signals which are subsequently output.
The enthalpy of humid air may be calculated from the following equations (A) and (B) when the temperature and pressure thereof are within the ranges in which every-day air conditioning units operate. EQU i=0.240t+(597.3+0.441t)x
(A) EQU x=0.622h.sub.s .multidot..psi./P-h.sub.s .multidot..psi. (B)
where
t: dry bulb temperature (.degree.C.), PA1 x: humidity ratio (kg/kg'), PA1 P: atmospheric pressure (mmHg), PA1 h.sub.s : saturated vapor pressure (mmHg), PA1 .psi.: relative humidity (%), PA1 i: enthalpy (Kcal/kg').
With equation (B), a complicated calculation is needed in which a value obtained by an approximate expression that has hitherto been disclosed, such as the IFC (International Formulation Committee) Formulation for Industrial Use must be substituted therein to obtain the saturated vapor pressure.
Accordingly, to obtain a value for the enthalpy of humid air using a conventional arithmetic unit, it has been necessary to obtain one other measured value, in addition to the dry bulb temperature. That is to say, conventional methods depend on the humidity ratio, wet bulb temperature, relative humidity, and dew point temperature and, whichever method is used, the measured values are used to calculate the enthalpy in accordance with equations (A) and (B) with an electronic computer. Any method depending on finding the dew point temperature or the humidity ratio has drawbacks including: a slow reaction speed and expensive sensing elements, and other methods depending on the wet bulb temperature, relative humidity, and dew point temperature having a disadvantage in that complicated equations must be solved.